Dynamically changing appearances for user interface elements during drag-and-drop operations

ABSTRACT

A user interface includes elements whose appearance dynamically changes in dependence upon functions associated with the elements. In the case of an icon that is the destination for a drag-and-drop operation, the image displayed for the icon changes in accordance with the object being dragged to it, to represent the task that will be performed as a result of the drag-and-drop operation. The appearance of other elements involved in drag-and-drop operations can also be varied, to reflect the task at hand. As a result, the user is provided with more intuitive feedback regarding the functions that will be performed by the computer as a result of a drag-and-drop operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityUnder 35 U.S.C. 120 to U.S. patent application Ser. No. 12/582,284,filed on Oct. 20, 2009, which is a continuation of and claims thebenefit of priority Under 35 U.S.C. 120 to U.S. patent application Ser.No. 10/100,067, filed on Mar. 19, 2002, and now issued as U.S. Pat. No.7,607,102, which in turn claims the benefit of priority Under 35 U.S.C.119(e) to U.S. Provisional Patent Application No. 60/363,875, filed onMar. 14, 2002, the benefit of priority of each of which is claimedhereby, and each of which is incorporated by reference herein in itsentirety.

FIELD OF THE INVENTION

The present invention generally relates to graphical user interfaces forcomputer systems, and more particularly to a user interface havingelements that provide an intuitive appearance to depict an operationbeing performed.

BACKGROUND OF THE INVENTION

An important aspect of any computer system is the interface that allow auser to input commands and data, and to receive the results ofoperations performed within me computer. In the area of personalcomputers, the graphical user interface (GUI) has become almostubiquitous. The most popular types of GUI are based upon a metaphor thatemulates the desktop environment. These types of GUI employ variousvisual elements to assist the user in managing information within thecomputer. Two fundamental elements are windows and icons. Windowsfunction as container elements, via which information is presented tothe user, and in which the user enters data to be input to the computer.The main, or root window, is commonly referred to as the “desktop” areaand functions as the primary display region. An icon comprises an imagethat is displayed on the desktop, or within another window, andrepresents a particular object. For instance, an icon may represent afile containing data or a program. An icon can also be employed torepresent a window that has been closed or minimized, container objectssuch as folders, and computer resources such as disk drives andprinters. Selecting an icon, for example by means of a mouse or othercursor control device, enables the user to access the information orresource represented by that icon.

Another feature of many GUIs, that facilitates the user's ability tointeract with the computer, is the drag-and-drop operation. An exampleof this type of operation is disclosed in U.S. Pat. No. 5,598,524, thedisclosure of which is incorporated herein by reference. In essence, thedrag-and-drop operation enables the user to perform a function by simplydragging an icon representing the object on which the function is to beperformed, and placing it upon another icon. For example, the user cancopy a file onto a disk by dragging the icon for the file onto the iconfor the disk. When the user releases the file icon while it ispositioned over the disk icon, the user interface recognizes this as acommand to copy the file onto the disk, and performs the required task.As another example, the user can cause a document to be printed, withouthaving to open an application program, by simply dragging the document'sicon onto a printer icon.

In some cases, the icon that forms the destination of a drag-and-dropoperation can represent different tasks, depending upon the nature ofthe object being dragged to the icon. An example of this can be seen,for example, in the case of the “trash” icon that is employed in theMacintosh Operating System, provided by Apple Computer, Inc. A userdrags an object to this icon when the user desires to remove the objectfrom the computer system. For instance, if a document is to be deletedfrom the computer's file system, the user drags the icon for thedocument to the trash icon. In consonance with the desktop metaphor, thetrash icon has the appearance of a garbage can, or wastebasket, toreinforce the user's understanding that the document being “deposited”on the trash icon is being disposed of.

In addition to the deletion of documents, files and folders, the trashicon can be employed to perform other functions. For example, the usercan drag an image of a removable disk to the trash icon, which causesthe disk to be automatically ejected from the disk drive of thecomputer. In this case, the user may not find the dragging of the diskicon to the image of a trash can to be intuitive. More particularly,placing an object in the trash can creates the impression that theobject is being thrown away. However, it is not the user's intention todispose of the removable disk, but merely to remove it from the computerhousing. Hence, a novice met may be reluctant drag the image of a diskto the trash can for fear that it may perform an unwanted action, suchas deleting all of the flies on the disk.

In some cases, therefore, the appearance of an element in a graphicaluser interface may not be consistent with a task that is beingperformed, particularly in those situations where the element isassociated with more than one task. It is an objective of the presentinvention, therefore, to provide a graphical user interface in which theimages associated with icons and other user interface elements provideintuitive feedback regarding the types of functionality associated withthose elements.

SUMMARY OF THE INVENTION

In pursuit of this objective, the present invention provides a userinterface having elements whose appearance dynamically changes independence upon characteristics of an object associated with adrag-and-drop operation. In one exemplary embodiment, if the element isan icon that is the destination for a drag-and-drop operation, the imagedisplayed for the icon changes in accordance with the object beingdragged to it, to represent the task that will be performed as a resultof the drag-and-drop operation or to represent a characteristic of theobject being dragged. The appearance of other elements involved indrag-and-drop operations can also be varied, to reflect the task athand. These other elements can include the icon for the object beingdragged, the cursor that is used to drag the icon, and control elementsassociated with resources involved in the task.

In the case of a trash icon, for example, its appearance can be mappedto the type of object being dragged to it. If the object is one that isto be deleted from the computer's file system, such as a document orfolder, the trash icon can have the appearance of a disposal container,such as a wastebasket or garbage can. If the dragged object is aphysical device that is to be removed from the computer, the trash iconcan display an image associated with ejecting the device from thesystem. Other functions associated with various objects that can bedragged to the trash icon can similarly cause the appearance of the iconto change to an image appropriate to that function.

As a result, the user is provided with more intuitive feedback regardingcharacteristics of objects being dragged and/or the functions that willbe performed by the computer as a result of a drag-and-drop operation.

Further features of the invention, and the advantages provided thereby,are explained in greater detail hereinafter, with reference to exemplaryembodiments of the invention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram of the general architecture of a computersystem in which the present invention can be implemented;

FIG. 2 illustrates a table containing data regarding different imagesassociated with an icon;

FIGS. 2A-2F illustrate the different images represented in the table ofFIG. 2;

FIGS. 3A-3C are representative examples of a display, illustratingdifferent appearances for a trash icon;

FIG. 4 is a mapping table of the different images for the trash icon;

FIG. 5 is a mapping table for a second embodiment of the invention; and

FIGS. 6A-6C are representative examples of a display, illustratinganother embodiment of the invention.

DETAILED DESCRIPTION

To facilitate an understanding of the features of the invention and theprinciples upon which it is based, exemplary embodiments are describedhereinafter in which the appearance of icons are dynamically varied inaccordance with a characteristic of an object being dragged to them,and/or the type of function that will be performed as a result of adrag-and-drop operation. It will be appreciated, however, that thereferences to icons are illustrative only. The principles which underliethe invention can be applied to any type of element employed within agraphical user interface, to provide users with more intuitiverepresentations of the characteristics of objects within a computersystem and/or the functions associated with those objects.

FIG. 1 is a block diagram of the components of a personal computer thatmay be involved in the implementation of the present invention.Generally, the graphical user interface forms part of the computer'soperating system 10. Examples of operating systems which provide agraphical user interface include the Macintosh® Operating System ofApple Computer, Inc., and the Windows® operating system provided byMicrosoft Corporation. The graphical user interface employs variousservices of the operating system that are responsible for generatinginformation that appears on the computer system's display 12, such as aCRT monitor or an LCD flat panel screen. These services include iconservices 14, which control the appearance and position of icons on thedisplay, and a windows manager 16, which controls the appearance, sizeand position of windows that appear on the screen. Each of theseservices communicates with a display manager 18 that also forms part ofthe operating system. The display manager is responsive to commandsreceived from the icon services and the windows manager, and generatesthe signals that control the display 12 to present the designatedimages.

User input to the computer system is accomplished by means of a keyboard20 and a cursor control device 22, such as a mouse, trackpad, pen, orthe like. As is known, the user employs the cursor control device 22 toposition a cursor appearing on the display, and actuates one or morecontrol buttons to select and move objects, as well as to activatecontrol elements to provide input. The movements of the cursor andactuation of the control buttons are fed as inputs to the appropriateelements of the operating system, to cause corresponding changes in theuser interface appearing on the display 12. For example, when the userclicks a button on the cursor control device 22, the location of thecursor is supplied to the icon services 14, along with an indicationthat a button has been clicked. If an icon is being displayed at thatlocation, the icon services can function to change the appearance of theicon, e.g. make it darker, to provide an indication that it has beenselected as a result of the user action.

For this purpose, the icon for any given object may have a family ofseveral different images. Some of these images may relate to differentstates of the object, whereas others may pertain to different userpreference items. FIG. 2 illustrates an example of a table storinginformation about the family of icon images stored in connection with aparticular object, in this case a document. The left side of the tableillustrates three different states for the icon, namely normal,highlighted and dimmed. The top of the table depicts two differentchoices for a user preference item. In this example, the user has theability to select whether large or small icons are to be displayed. Eachcombination of state and size has a stored icon image associated withit. FIG. 2A illustrates the image for the icon in its normal state andlarge size, whereas FIG. 2B illustrates the normal state and small size.FIGS. 2C and 2D illustrate the highlighted state of the icon, for thelarge and small sizes, respectively. FIGS. 2E and 2F illustrate thedimmed state of the icon, again for the large and small sizes. Independence upon the state of the object associated with an icon and theuser-chosen size, the icon services 14 selects the appropriate image andprovides it to the display manager 18.

In accordance with the present invention, another dimension of variationis provided for icon images to reflect the characteristics of adrag-and-drop operation. In one embodiment of the invention, the iconrepresenting the destination for a drag-and-drop operation has itsappearance varied in dependence upon the task associated with thedrag-and-drop operation.

For example, with references to FIGS. 3A-3C, various types of objectscan be dragged to a trash icon 30, to remove them from the computersystem. For instance, as depicted in these figures, the user can drag adocument 32, a folder 34, a floppy disk 36 or a compact disk (CD) 38 tothe trash icon 30. In the case of documents 32 and folders 34, theeffect of dragging them to fee trash icon is to delete them from thecomputer's file system. For this purpose, an appropriate image for theicon 30 is that of a container associated with the disposal of objects,such as a wastebasket as shown in FIG. 3A, or a garbage can. In the caseof the floppy disk 36 and the CD 38, however, the act of dragging theiricons to the trash icon 30 does not result in a deletion of thoseobjects. Rather, it causes them to be ejected from the correspondingdrive mechanisms in the computer. In this case, the image of awastebasket or garbage can may not be suitable, since it does notprovide the most appropriate metaphor for the task being implemented. Inaccordance with the present invention, therefore, when one of thesetypes of objects is being dragged to the trash icon, the image for theicon is changed to symbolize the nature of the object, which determinesthe action that will be undertaken when the object is dropped onto theicon. FIG. 3B illustrates the situation in which the icon for the floppydisk 36 is being dragged to the trash. In this case, it can be seen thatthe appearance of the icon 30 has been changed to the image of a symbolwhich represents the ejection of an object from the system.

In one implementation of the invention, the image that is displayed forthe destination of a drag-and-drop operation can be based upon the typeof object being dragged. In this regard, the operating system storestype information for each object that is stored in the computer system'smemory. In the example described above, the determination of theappropriate image to display for the trash icon can be based uponwhether the object is a physical object, such as a removable storagemedium, or an electronic object, for example a file system object suchas a folder or a file. For this purpose, the information that is storedin the icon services 14 for each icon can include a flag, or bit, thatindicates whether multiple “personalities” are associated with the icon.If so, a mapping table is provided for the icon, that indicates thedifferent images that are respectively displayed in association with thevarious personalities. An example of such a mapping table for the trashicon is illustrated in FIG. 4. The left column of the table depicts thedifferent types of objects that can be dragged to the icon. In the caseof the trash icon, for example, the objects are classified as physicalor electronic. Each object type has an associated image that is storedin the icon services, and the mapping table includes a pointer to thatimage, e.g. IMG3A or IMG3B.

In operation, one of the images can be designated as the default image,and is displayed at all times except when an object of a predeterminedtype is being dragged. For instance, in the case of the trash icon, thedefault image could be the wastebasket depicted in FIG. 3A. This imageis displayed at all times, except when the user is dragging an icon fora physical object. When the user selects a physical object, thisinformation is provided to the icon services, which checks whether anyicon currently being displayed has its flag set to indicate multi-imagecapability. If so, the icon image table for that icon is checked, todetermine whether the object that has just been selected is of the typethat requires a change in appearance. If so, the image data for the newappearance is retrieved and provided to the display manager 18, to causethe icon to change appearance, as illustrated in FIG. 3B.

The change in appearance can occur as soon as the object is selected.Alternatively, it may be preferable to wait until a selected object isbeing dragged by the user before determining whether to change theappearance of potential destination icons, to thereby minimize thefrequency of appearance changes.

The foregoing example illustrates the situation in which two differentfunctions are associated with the trash icon, namely to delete a filesystem object or eject a physical object such as a disk. It will beappreciated, however, that the number of functions is not limited, andeach function can have a separate icon image associated with it. Withfurther reference to the trash icon, it is possible to perform differentkinds of operations on an object to be removed, depending upon the stateof the object. For example, the CD icon 38 may represent a blank CD thatthe user has inserted into computer's disk drive. The user can drag theicons for one or more documents 32 onto the icon for the CD 38, toindicate that the user desires to store copies of the document on theCD. However, each file is not automatically copied, or “burned” onto theCD as it is dropped onto the icon 38. Rather, it is necessary for theuser to explicitly indicate that the burn operation is to take place,preferably after all of the desired files have been dragged to the CDicon 38. If the user drags the CD icon 38 to the trash icon 30 beforeinitiating the burn operation, the image that is displayed for the trashicon can be a burn symbol, as illustrated in FIG. 3C. This image advisesthe user that there are files to be burned onto the CD before it isejected from the computer. If the user completes the drag-and-dropoperation, a dialog window can be displayed, to have the user confirmthat the burn operation should take place before the CD is ejected.

FIG. 5 illustrates an example of an icon image mapping table for thisembodiment of the invention. In this case, the operating systemdistinguishes between different types of removable physical objects. Ifthe object is a floppy disk, the eject symbol image is displayed, as inthe example of FIG. 3B. If, however, the object is a CD, a furtherdetermination is made with respect to the state of the CD, namelywhether there is information to be burned onto it. This might bedetermined, for example, by reference to the state of an action flagassociated with the icon. If the flag is set, indicating that there isinformation to be stored on the CD, the burn symbol image, depicted inFIG. 3C, is displayed. Otherwise, the eject symbol image of FIG. 3B isdisplayed.

While the foregoing embodiments of the invention have been describedwith reference to the trash icon, it will be appreciated that theprinciples of the invention can be employed for any user interfaceelement associated with a drag-and-drop operation. For instance, an iconmight be associated with the computer's file system, such as the Findericon associated with the Macintosh® Operating System. An example of afile system icon 40 is illustrated in FIG. 6A. When a user drags a file42 to this icon, the file is stored in the computer's file system.Depending upon the type of file, it can be stored in different folderswithin the file system. In accordance with the present invention, theimage that is displayed for the file system icon can change, inaccordance with the area in which the file is to be stored. Forinstance, as shown in FIG. 6B, if the user drags a text file 32 to thefile system icon, the icon 40 might appear as a “Documents” folder, toindicate that the file is being stored in that folder. Conversely, ifthe user drags a movie file 44 to the file system icon 40, theappearance of that icon can change to a “Movies” folder, as shown inFIG. 6C. Thus, rather than generically informing the user that the fileis being stored within the file system, the change in appearance of thefile system icon 40 provides the user with better feedback regarding theprecise location at which the file is being stored.

As another example, the user may drag a file to a printer icon, to causethe file to be printed. Depending upon the nature of the file, it may besent to one of several different printers. For example, a black andwhite text file may be sent to a monochrome printer, whereas a colorgraphics file may be sent to a higher resolution, color printer. In thissituation, the icon for the printer can change appearance, to indicatethe particular printer to which the dragged file will be sent.

From the foregoing, therefore, it can be seen that the present inventionprovides the user with more intuitive feedback regarding the tasks thatare performed as a result of a drag-and-drop operation. In theseexamples, the appearance of the icon which functions as the destinationfor the drag-and-drop operation is changed, in accordance with theresult to be accomplished. It will be appreciated, however, that otherelements of the user interface can have similar behavior. For instance,it may be preferable to change the appearance of the icon being dragged,in addition to, or lieu of, the destination icon. Likewise, the cursorthat is used to drag the icon can change its appearance, to provide anindication of the operation being performed.

In a further aspect of the invention, the dynamic icon functionality canbe extended to application programs that are aware of this feature inthe user interface. More particularly, an application having such anawareness can provide the icon services with an image that is to bedisplayed by a particular icon whenever an object associated with thatapplication is selected. For instance, the developer of a drawingprogram may create an image of an eraser that is to be employed whenevera drawing created with that program is to be deleted, to symbolize aslate being wiped clean. When the drawing program is installed on acomputer, it can supply this image to icon services along with anidentification of the icon to which it is to be applied, i.e. the trashicon, and the type of object with which it is to be associated, e.g.files with the extension “dwg”. This information is added to the tablessuch as those depicted in FIGS. 4 and 5. Subsequently, when a drawingobject is selected, the image of the eraser is displayed for the trashicon.

It will be appreciated by those of ordinary skill in the art that thepresent invention can be embodied in other forms without departing fromthe spirit or essential characteristics thereof. The presently disclosedembodiments are therefore considered in all respects to be illustrativeand not restrictive. The scope of the invention is indicated by theappended claims, rather than the foregoing description, and all changesthat come within the meaning and range of equivalence thereof areintended to be embraced therein.

The invention claimed is:
 1. A method comprising: at a device with adisplay and one or more input devices: displaying, on the display, agraphical user interface that includes a first selectable graphicalelement, a second selectable graphical element, and a target object,wherein: the first selectable graphical element is associated with afirst type of operation that is capable of being performed upon a firstobject through interaction of the first selectable graphical elementwith the target object; the second selectable graphical element isassociated with a second type of operation, different from the firsttype of operation, that is capable of being performed upon a secondobject through interaction of the second selectable graphical elementwith the target object; and the target object has a first appearance;while displaying, on the display, the graphical user interface thatincludes the first selectable graphical element, the second selectablegraphical element, and the target object with the first appearance,detecting, via the one or more input devices, a user input selecting arespective selectable graphical element displayed in the graphical userinterface; and in response to detecting the user input: in accordancewith a determination that the respective selectable graphical element isthe first selectable graphical element, changing appearance of thetarget object from the first appearance to a second appearance thatcorresponds to the first type of operation that is capable of beingperformed upon the first object through interaction between the firstselectable graphical element and the target object; and in accordancewith a determination that the respective selectable graphical element isthe second selectable graphical element, maintaining the appearance ofthe target object as the first appearance, wherein the first appearancecorresponds to the second type of operation that is capable of beingperformed upon the second object through interaction between the secondselectable graphical element and the target object.
 2. The method ofclaim 1, further comprising: performing the first type of operation onthe first object in response to detecting movement of the firstselectable graphical element upon the target object in the graphicaluser interface.
 3. The method of claim 2, wherein the first selectablegraphical element and the target object are respective icons, andwherein the user input is a drag-and-drop operation enabling movement ofthe first selectable graphical element over the target object in thegraphical user interface.
 4. The method of claim 1, wherein changing theappearance of the target object includes changing the appearance of thetarget object from a first icon to a second icon, and wherein changingthe appearance occurs in response to selection of the first selectablegraphical element in the graphical user interface.
 5. The method ofclaim 1, wherein the target object represents a destination to which thefirst object can be moved or copied.
 6. The method of claim 1, whereinthe first type of operation is used to perform an action for removal ofthe first object from a computer system.
 7. The method of claim 1,wherein the first type of operation is used to perform an action forstorage of the first object in a computer system.
 8. A computing device,comprising: a display device; one or more input devices; a processor;and a memory configured for storing instructions for execution that whenexecuted by the processor cause the computing device to: generate, fordisplay on the display device, a graphical user interface that includesa first selectable graphical element, a second selectable graphicalelement, and a target object, wherein: the first selectable graphicalelement is associated with a first type of operation that is capable ofbeing performed upon a first object through interaction of the firstselectable graphical element with the target object; the secondselectable graphical element is associated with a second type ofoperation, different from the first type of operation, that is capableof being performed upon a second object through interaction of thesecond selectable graphical element with the target object; and thetarget object has a first appearance; while the graphical user interfacethat includes the first selectable graphical element, the secondselectable graphical element, and the target object with the firstappearance is displayed on the display device, detecting, via the one ormore input devices, a user input selecting a respective selectablegraphical element displayed in the graphical user interface; and inresponse to detecting the user input: in accordance with a determinationthat the respective selectable graphical element is the first selectablegraphical element, changing appearance of the target object from thefirst appearance to a second appearance that corresponds to the firsttype of operation that is capable of being performed upon the firstobject through interaction between the first selectable graphicalelement and the target object; and in accordance with a determinationthat the respective selectable graphical element is the secondselectable graphical element, maintaining the appearance of the targetobject as the first appearance, wherein the first appearance correspondsto the second type of operation that is capable of being performed uponthe second object through interaction between the second selectablegraphical element and the target object.
 9. The computing device ofclaim 8, wherein the target object is associated with storage operationsfor electronic objects in the computing device, and wherein the firstappearance and the second appearance designate different storageoperations.
 10. The computing device of claim 9, wherein the differentstorage operations include different destinations for the electronicobjects.
 11. The computing device of claim 8, wherein the firstappearance and the second appearance are used to indicate respectivefile system destinations for file system operations initiated frominteraction of the first selectable graphical element or the secondselectable graphical element with the target object.
 12. The computingdevice of claim 8, wherein the user input selecting the respectiveselectable graphical element displayed in the graphical user interfaceresults in a selection of the first object and a selection of a taskassociated with the first object.
 13. A computer readable storage mediumcomprising a computer program operable in a computing device, thecomputer program comprising instructions for: displaying, on a display,a graphical user interface that includes a first selectable graphicalelement, a second selectable graphical element, and a target object,wherein: the first selectable graphical element is associated with afirst type of operation that is capable of being performed upon a firstobject through interaction of the first selectable graphical elementwith the target object; the second selectable graphical element isassociated with a second type of operation, different from the firsttype of operation, that is capable of being performed upon a secondobject through interaction of the second selectable graphical elementwith the target object; and the target object has a first appearance;while displaying, on the display, the graphical user interface thatincludes the first selectable graphical element, the second selectablegraphical element, and the target object with the first appearance,detecting, via one or more input devices, a user input selecting arespective selectable graphical element displayed in the graphical userinterface; and in response to detecting the user input: in accordancewith a determination that the respective selectable graphical element isthe first selectable graphical element, changing appearance of thetarget object from the first appearance to a second appearance thatcorresponds to the first type operation that is capable of beingperformed upon the first object through interaction between the firstselectable graphical element and the target object; and in accordancewith a determination that the respective selectable graphical element isthe second selectable graphical element, maintaining the appearance ofthe target object as the first appearance, wherein the first appearancecorresponds to the second type of operation that is capable of beingperformed upon the second object through interaction between the secondselectable graphical element and the target object.
 14. The computerreadable storage medium of claim 13, wherein the computer programfurther comprises instructions for: performing the first type ofoperation upon the first object in response to detecting movement of thefirst selectable graphical element over the target object in thegraphical user interface.
 15. The computer readable storage medium ofclaim 14, wherein the movement of the first selectable graphical elementover the target object is facilitated by a drag-and-drop operation inthe graphical user interface to place the first selectable graphicalelement over the target object.
 16. The computer readable storage mediumof claim 13, wherein changing the appearance of the target object fromthe first appearance to the second appearance is performed in responseto movement of the selectable graphical element.
 17. The computerreadable storage medium of claim 13, wherein the appearance of thetarget object is changed to represent a destination to which the firstobject can be moved or copied.
 18. The computer readable storage mediumof claim 13, wherein the target object is associated with removal of aselected object from the computing device, wherein the appearance of thetarget object is changed to one of a first image or a second image,wherein the first image and the second image correspond to whether theselected object is a physical object or an electronic object associatedwith the computing device.
 19. The computer readable storage medium ofclaim 13, wherein the first type of operation includes a storageoperation in the computing device, wherein the appearance of the targetobject is changed to designate a particular storage operation with thefirst object.
 20. The computer readable storage medium of claim 19,wherein the storage operation pertains to different respectivedestinations in the computing device.
 21. The method of claim 1, whereinthe second type of operation is unavailable for performance upon thefirst object.
 22. The computing device of claim 8, wherein the secondtype of operation is unavailable for performance upon the first object.23. The computer readable storage medium of claim 13, wherein the secondtype of operation is unavailable for performance upon the first object.